1. Field of the Invention
The present invention relates to a nitride semiconductor laser device having a nitride semiconductor laser chip mounted on a mount member. In the present specification, a nitride semiconductor denotes a compound of the composition AlxGayInzN (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1). Here, of the nitrogen atoms contained in this nitride semiconductor, about 10% or less (which must have a hexagonal crystal structure) may be replaced with any of the elements As, P, and Sb. Moreover, the nitride semiconductor may be doped with Si, O, Cl, S, C, Ge, Zn, Cd, Mg, or Be.
2. Description of the Prior Art
Semiconductor laser devices produce intense light with high monochromaticity, and thus the laser light they emit can be condensed to an extremely small spot. For these advantages, semiconductor laser devices are used, for example, as light sources in optical pickup parts for use in drives for recording media such as optical and magneto-optical discs with which the recording and reading of data are achieved by irradiating them with light. In particular, nitride-based semiconductor laser devices, which produce light of short wavelengths with high output, are eagerly developed as optical pickup devices to supplant red semiconductor laser devices for application in drives for high-density recording media such as DVDs.
An example of a nitride semiconductor laser chip for use in such nitride semiconductor laser devices is proposed in Japanese Patent Application Laid-Open No. H11-340571. FIG. 10 shows the structure of the nitride semiconductor laser chip disclosed in this publication. The nitride semiconductor laser chip shown in FIG. 10 has, on the top surface of a nitride semiconductor substrate 500, an n-type clad layer 501, an n-type optical guide layer 502, an active layer 503, a p-type optical guide layer 504, a p-type clad layer 505, a p-type contact layer 506, an insulating film 507, and a p-electrode 508 laid in this order, and has, on the bottom surface of the nitride semiconductor substrate 500, an n-type contact layer 509 and an n-electrode 510 laid in this order.
The nitride semiconductor laser chip structured as shown in FIG. 10 is mounted on a stem to produce a nitride semiconductor laser device. Specifically, as shown in FIG. 3, the nitride semiconductor laser chip 103 is mounted on a mount member 102 placed on a chip mount portion 101 formed on the stem 100. Here, the nitride semiconductor laser chip 103 is mounted so that its n-electrode 510 is kept in contact with the mount member 102. Moreover, to fix the nitride semiconductor laser chip 103 on the mount member 102, the mount surface of the mount member 102 is metalized with Au, and the n-electrode 510 is bonded to it by thermal compression. On the other hand, the p-electrode 508 is electrically connected to a pin 105b by a wire 104 of Au. Another pin 105a is electrically connected to the chip mount portion 101 and to the mount member 102. The pins 105a and 105b are electrically insulated from the stem 100.
In the nitride semiconductor laser device structured as described above, when voltages of different potentials are applied to the pins 105a and 105b, and thus to the n-electrode 510 and the p-electrode 508 of the nitride semiconductor laser chip 103, the nitride semiconductor laser chip 103 starts laser operation.
In GaAs-based semiconductor laser devices conventionally used, the mount member (corresponding to the mount member 102 shown in FIG. 3) on which a semiconductor laser chip is mounted is made of a material (for example, SiC) that has high thermal conductivity and that has a thermal expansion coefficient as close as possible to that of GaAs used as the substrate of the semiconductor laser chip. This is because, in GaAs-based semiconductor laser devices, if the mount member is made of a material of which the thermal expansion coefficient greatly differs from that of GaAs used in the semiconductor laser chip, when the semiconductor laser chip is soldered to the mount member, high stress occurs in the semiconductor laser chip, causing defects in and shortening the laser operating lifetime of the semiconductor laser devices.
On the other hand, nitride semiconductor laser devices produced by conventional techniques have short laser operating lives. They have short laser operating lives even when their mount member, shown in FIG. 3, is made of SiC as in GaAs-based semiconductor laser devices.